We demonstrate a four-channel on-chip true-time-delay module based on a photonic crystal waveguide array. Using the photonic crystal taper to minimize the coupling loss, the delay lines with 1–3 mm long photonic crystal waveguides can operate up to a group index ng ∼ 23 without significant loss. The large group velocity dispersion enables continuous and wavelength-tunable time delays. Measurements show a highly linear phase-frequency relation, highest time delay up to 216.7 ps, and large tuning ranges of 58.28 ps, 115.74 ps, and 194.16 ps for 1–3 mm delay lines. The chip-scale true-time-delay module occupies only 0.18 mm&#178; area and can provide ±44.38° steering for an X-band phased-array-antenna.